Rotor for a turbomachine

ABSTRACT

A rotor for a turbomachine is provided. The rotor includes a shaft and a longitudinal bearing disk arranged thereon as an element for an axial bearing for axially supporting the shaft. The longitudinal bearing disk includes first and second contact surfaces. The first contact surface is cylindrical for radial support on the shaft. The second contact surface is conical for self-centering on the shaft. Advantageously, such a rotor may be used for operation with chemically aggressive gases and can be operated at substantially high rotational speeds.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International ApplicationNo. PCT/EP2010/054210, filed Mar. 30, 2010 and claims the benefitthereof. The International Application claims the benefits of Germanapplication No. 10 2009 015 859.6 filed Apr. 1, 2009. All of theapplications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to a rotor for a turbomachine, having a shaft anda longitudinal bearing disk, which is arranged on said shaft, as anelement for an axial bearing for axially bearing the shaft.

BACKGROUND OF INVENTION

Working elements, for example in the form of paddle wheels, are arrangedon a shaft of a turbomachine, such as a gas or steam turbine or aturbocompressor, a stationary pressure difference between an inlet andoutlet of the turbomachine being increased or decreased by said workingelements. A large force is transmitted onto the shaft in the axialdirection of the shaft by operation of the working elements, said forcebeing absorbed by an axial bearing. The axial bearing comprises alongitudinal bearing disk, which is part of the rotor, and bearingelements on the stator, the longitudinal bearing disk being supported onsaid bearing elements—by magnetic forces or by a lubricated slidingaction depending on the type of bearing.

In the case of industrial turbomachines, in particular in the case ofthose which are used in the chemical industry, rotation speeds in theregion of several 10000 revolutions per minute are sometimes required.Rotation speeds of such a high level require enormous strength both ofthe working elements and of the longitudinal bearing disk which has arelatively large radius for absorbing and passing on a high axial thrustand therefore is subject to large centrifugal forces. In order to ensurethe required high strength, high-alloy steels with a yield strength ofaround 1000 N/mm2 are usually used.

If a turbomachine, in particular in the industrial sector, comes intocontact with aggressive gases, for example during compression ofhydrogen sulfide-containing gases, the working elements and also thelongitudinal bearing disk are chemically corroded and therefore theirstrength is impaired. However, steels which are not corroded by hydrogensulfide only have a maximum strength of 700 N/mm2. Therefore,turbomachines which come into contact with hydrogen sulfide or similarlyaggressive gases can be operated only at relatively low rotation speedsas machines which are not designed for exposure to such aggressivechemical gases.

SUMMARY OF INVENTION

It is an object of the present invention to specify a rotor for aturbomachine, which rotor can be designed for operation with chemicallyaggressive gases and can be operated at high rotation speeds in theregion of greater than 10000 revolutions per min.

This object is achieved by virtue of a rotor of the type cited in theintroductory part, in which, according to the invention, thelongitudinal bearing disk has a first, cylindrical contact face forradial mounting on the shaft and a second, conical contact face forautomatic centering on the shaft.

In this case, the invention proceeds from the consideration thatlongitudinal bearing disks of known design are mounted on the shaft ofthe rotor by means of a hydraulic shrink-fit. In this case, thelongitudinal bearing disk is hydraulically widened and pushed onto aslightly conical contact face of the shaft against a stop. A shaft nutholds the shrunk-on longitudinal bearing disk axially in position. Inorder to prevent the longitudinal bearing disk slipping on the contactface of the shaft, said longitudinal bearing disk still has to be ableto retain its stable press-fit on the contact face even when subject tostrong centrifugal forces, this requiring the press-fit to be very fine.As a result, the steel of the longitudinal bearing disk is subject to avery high level of stress.

If a stable connection is also achieved without a shrink-fit, the forceson the longitudinal bearing disk created by the shrinking process arenot applicable and said longitudinal bearing disk can use all itsstrength to withstand the centrifugal forces. By reducing the producedstresses on account of the stresses from the shrink-fit being removed,materials for the longitudinal bearing disk which are suitable forcompressing hydrogen sulfide can also be used at high rotation speeds.

The longitudinal bearing disk can be held radially in its position bythe first, cylindrical contact face and therefore an unbalance can beavoided. The second, conical contact face serves to transmit thetangential forces from the longitudinal bearing disk to the shaft, sothat said longitudinal bearing disk does not rotate relative to theshaft. In order to transmit the forces, the longitudinal bearing disk isexpediently pressed against a mating face of the shaft or a componentwhich is attached to said shaft by a shaft nut by way of its conicalcontact face.

The turbomachine is, in particular, a turbocompressor. The invention canbe applied particularly advantageously to a longitudinal bearing disk ofthe kind which is part of a magnet bearing. On account of the magnetbearing, the longitudinal bearing disk is of relatively large design andis therefore subject to a high level of mechanical stress in the eventof fast rotations. Particularly low-friction bearing can be achieved bymagnetic bearing.

The conical contact face serves for automatic centering of thelongitudinal bearing disk on the shaft. The conical contact faceexpediently does not directly adjoin the first, cylindrical contactface, in order to avoid a sharp edge which could damage the shaft whenthe longitudinal bearing disk is pushed onto the shaft. Therefore, thetwo contact faces are expediently spaced apart from one another, forexample by a flat intermediate face, such as a chamfer, or can beconnected to one another by a rounded portion.

In an advantageous embodiment of the invention, the second contact faceis conical in an offset manner relative to radial compression of thelongitudinal bearing disk. As a result, widening of the longitudinalbearing disk is avoided when the contact faces are compressed, andtherefore the longitudinal bearing disk is mechanically protected.Compression counteracts the centrifugal forces and therefore has anadvantageous effect on the strength of the longitudinal bearing disk.

In order to simultaneously transmit tangential forces, the conicalcontact face and its mating face can be designed as a Hirth connection.However, this refinement has the disadvantage that it is associated withhigh outlay on production. Therefore, conicity in the form of atruncated cone face is preferred, in the case of which force istransmitted from the contact face to the mating face by a force-fittingconnection, that is to say by adhesion. In this case, the force withwhich the longitudinal bearing disk, at its conical contact face, ispressed against the mating face is selected to be so large that theresulting force on the contact face can transmit the required startingtorques without the second contact face sliding on its mating face byfriction moments.

The second contact face is advantageously designed with an angle ofinclination relative to the radial direction of the shaft of between 5°and 30°. The greater the angle of inclination, the higher the frictionmoment between the contact face and mating face—given the sameprestressing force—, however, also together with a higher mechanicalstressing of the longitudinal bearing disk and the shaft. The forceswhich occur can be adapted, as is respectively required, by optimizingthe angle of inclination.

The longitudinal bearing disk is expediently mounted such that anincreasing bearing force acts on the second contact face as the rotationspeed increases. This can be achieved, in particular, by the offsetconicity of the second contact face. As the rotation speed increases,the increasing radial force leads to an increasing contact pressure bythe second contact face against its mating face, as a result of whichthe torque which can be transmitted increases, said torque beinggenerated by the friction action of the two contact faces on oneanother.

An increase in the temperature of the longitudinal bearing diskadvantageously leads to an increasing bearing force of the secondcontact face. This can counteract a reduction in frictional forces onthe contact faces.

It is also advantageous when the longitudinal bearing disk is mounted onthe shaft without stress by way of the first contact face. Thelongitudinal bearing disk can be mechanically protected and therefore bedriven at high rotation speeds. Freedom from stress is provided when thelongitudinal bearing disk can be pushed onto the shaft by hand for thepurpose of mounting the first contact face on its corresponding matingface.

Secure mounting of the longitudinal bearing disk and reliable operationof the rotor can be achieved when the second contact face rests againsta conical mating face which is formed in the shaft. The conical matingface is therefore directly part of the shaft, and therefore a shaft ringor a similar component can be dispensed with.

The second contact face is advantageously an end face of the bearingdisk, with an end face being understood to mean a face with aninclination of less than 45° relative to the radial direction of theshaft.

In order to avoid an unbalance of the longitudinal bearing disk afterremoval and re-mounting, a rotation-prevention means is expedientlyprovided, said rotation-prevention means prespecifying a fixedtangential position for the longitudinal bearing disk on the shaft. Therotation-prevention means can also absorb tangential forces, which areproduced, for example, when the rotor is started or by friction of thelongitudinal bearing disk in the bearing, during operation. However, itis expedient for the rotation-prevention means to be designed to be assmall as possible in order to not have too great an adverse effect onthe stability of the longitudinal bearing disk. Therefore, it isadvantageous when the second contact face is intended to transmit atleast the major portion of the tangential forces from the shaft to thelongitudinal bearing disk. The major portion is more than 50% of thetangential forces.

In a further advantageous embodiment of the invention, the rotor isequipped with a rotation-prevention means which holds the longitudinalbearing disk in a desired tangential position by a positive-lockingconnection. A change in the balance states after removal and re-mountingcan be avoided.

The positive-locking connection can be established directly between thelongitudinal bearing disk and the shaft, for example by atongue-and-groove connection in or in the vicinity of the first contactface. However, the strength of the longitudinal bearing disk is notinconsiderably adversely affected by a recess in a face of thelongitudinal bearing disk which faces radially inward. It is thereforeadvantageous when a positive-locking element of the rotation-preventionmeans engages in an end face of the longitudinal bearing disk. A recessin the end face leads to a considerably lower mechanical stress on thefoot of the longitudinal bearing disk in the event of fast rotations.The end face is expediently arranged opposite the second contact face.The second contact face can be designed to be free of cavities andentirely for transmitting friction.

The rotation-prevention means advantageously comprises arotation-prevention ring which at least indirectly forms apositive-locking connection with the longitudinal bearing disk and formsat least an indirect positive-locking connection with the shaft in thesame direction. Positive transmission of force from the longitudinalbearing disk to the rotation-prevention ring can be continued in asimple manner in the same direction, for example in the tangentialdirection, as to the shaft. The production of the elements can be keptsimple when the two positive-locking connections are each formed by apositive-locking element which engages in the elements which areconnected in a positive-locking manner. The positive-locking connectionbetween the rotation-prevention ring and the shaft is expedientlyachieved by a feather key which engages in a groove in therotation-prevention ring and the shaft. For balance reasons, twopositive-locking elements are expediently provided for each of the twopositive-locking connections.

The feather key and the positive-locking element are expedientlyarranged so as to be tangentially offset to one another; when there aretwo positive-locking elements and two feather keys, which areadvantageously mounted opposite one another in each case,positive-locking elements and feather keys are advantageously arrangedat an angle of 90° in relation to one another.

A large increase in temperature may also cause the longitudinal bearingdisk to expand to a particularly great extent in the axial direction.Under certain circumstances, the second contact face presses against itsmating face with an undesirably great force, as a result of which highmechanical stress is produced. In order to reduce this stress, the rotorexpediently comprises a spring means for absorbing bearing forces on thesecond contact face. The spring means can obtain its spring effect byvirtue of a recess which is compressed in the event of a spring-likemovement. The recess can be formed in the longitudinal bearing disk orin the component which forms the mating face to the conical contact faceof the longitudinal bearing disk, in particular directly in the shaft.

DETAILED DESCRIPTION OF INVENTION

The invention will be explained in greater detail with reference to anexemplary embodiment which is illustrated in a drawing. The singlefigure in said drawing shows a sectional illustration of a detail of arotor 2 of a turbomachine in the form of an axial compressor. The rotor2 comprises a shaft 6 which runs in the axial direction 4 and to which alongitudinal bearing disk 8 is attached. The longitudinal bearing disk 8is part of an axial bearing 10, two magnet poles 12 of said axialbearing, said magnet poles supporting the longitudinal bearing disk 8 inthe axial direction 4, being schematically illustrated for betterunderstanding. The axial bearing 10 is therefore a magnet bearing forholding the shaft 6 in an intended axial position.

The longitudinal bearing disk 8 is provided with a first,hollow-cylindrical contact face 14 which rests on a likewise cylindricalmating face 16 of the shaft 6. The bearing which is formed by thecontact face 14 and the mating face 16 holds the longitudinal bearingdisk on the shaft 6 without play in the radial direction 18. Thelongitudinal bearing disk 8 has a first end face 20 and a second endface which is opposite said first end face and is designed as a secondand conical contact face 22. The contact face 22 rests on a mating face24 which is formed directly in the material of the shaft 6.

The contact face 22 is provided with an angle of inclination α of 25°,with the contact face 22 being designed to be offset, that is to saysuch that the mating face 24 engages somewhat beyond the longitudinalbearing disk 8 in the region of the contact face 22. As a result, thelongitudinal bearing disk 8 is compressed when the longitudinal bearingdisk 8 is axially braced, and pressed onto the shaft 6 against acentrifugal force effect. The conicity of the contact face 22 has theeffect of the longitudinal bearing disk 8 being automatically centeredon the shaft 6, this assisting in centering the longitudinal bearingdisk 8 by contact between the faces 14, 16.

In order to avoid an edge of the longitudinal bearing disk 8 buttingagainst the shaft material, a chamfer 26 is formed between the twocontact faces 14, 22, with a rounded portion between the contact faces14, 22 also being expedient. A cavity 28 in the shaft material leads toa reduction in the stress peaks in the material of the shaft 6 in theevent of a high contact-pressure force of the longitudinal bearing disk8 against the shaft 6 in the axial direction 4. For the same purpose,cavities 30 are made in both sides of the longitudinal bearing disk 8,with the cavities 28, 30 advantageously being formed by calculationusing the finite element method in order to subject the cavities 28, 30to as uniform a material stress as possible along the wall.

A shaft nut 32, which is connected to the shaft 6 by a thread 34 in apositive-locking manner, is braced against a rotation-prevention ring 36in order to mount the longitudinal bearing disk 8, saidrotation-prevention ring pressing the longitudinal bearing disk againstthe corresponding mating face 24 by way of its contact face 22. Aprestressing force FV which is applied by the shaft nut 32 is selectedto be of such a magnitude that the normal force FN of the contact face22 on the mating face 24, said normal force resulting from an axialforce FAX and the angle of inclination α, produces such a great frictionaction that the longitudinal bearing disk 8 does not slip on the shaft 6in the tangential direction when the rotor 2 is started.

As the rotation speed increases, the increasing radial force FR leads toan even greater normal force FN. As a result, the transmissible torqueis automatically increased, this being generated by the friction actionof the longitudinal bearing disk 8 on the mating face 24. An increase intemperature in the longitudinal bearing disk 8 also produces a highernormal force FN, and therefore a higher transmissible torque, on accountof the expansion of the longitudinal bearing disk 8 in the axialdirection 4. The resulting axial force FAX is absorbed by the shaft nut32.

In order to avoid an excessively high normal force FN or axial force FAXin the event of a very high temperature of the longitudinal bearing disk8, and therefore damage to the material of the longitudinal bearing disk8 or shaft 6, a recess 38 is made in the shaft 8. This recess runsaround the shaft 6 and thereby forms a slightly elastic web 40 whichlimits the contact-pressure force of the two contact faces 22, 24 on oneanother to a level which is safe for the materials.

Mounting or removal of the longitudinal bearing disk 8 can be performedin a simple manner by the longitudinal bearing disk 8 being pushed intothe shaft 6 or being removed from said shaft by hand. In order to avoidan unbalance after removal, the longitudinal bearing disk 8 should bereturned to its original tangential position on the shaft 6 when it isre-mounted. In order to ensure this, the rotation-prevention ring 36 isarranged between the shaft nut 32 and the longitudinal bearing disk 8,said rotation-prevention ring being connected to the longitudinalbearing disk 8 in a positive-locking manner by means of twopositive-locking elements 42 in the form of bolts in the tangentialdirection, that is to say in the circumferential direction.

The positive-locking elements 42, of which only one is illustrated forthe sake of clarity, the other being considered to be offset through180°, that is to say in relation to the rotation axis 44 of the shaft16, engage in the end face 20 of the longitudinal bearing disk 8, sothat the contact face 14 of the longitudinal bearing disk 8 continues tonot be adversely affected. Both the rotation-prevention ring 36 and theshaft 6 are provided with a groove 46 and, respectively, 48 which areheld in position relative to one another in the tangential direction bymeans of a feather key 50 which is designed as a rectangular steel bar.In this way, an indirect positive-locking connection is establishedbetween the shaft 6 and the longitudinal bearing disk 8 in such a waythat the longitudinal bearing disk 8 can be mounted only in a presetposition in the tangential direction and remains in this position.

The feather key 50 is also provided in duplicate, with the two featherkeys 50 likewise being arranged opposite one another in relation to therotation axis 44. The feather keys 50 are arranged in a manner offsetthrough 90° in relation to the positive-locking elements 42 in thetangential direction. Solely for the sake of simplifying the figures,said feather keys are shown in the same sectional plane, in order to beable to dispense with the need for a further sectional illustrationthrough the rotor 2 rotated through 90° about the rotation axis 44.

The positive-locking element 42 and the feather key 50 can be designedas additional security means against tangential rotation of thelongitudinal bearing disk 8 on the shaft 6. However, in order to keepthe stability and thus the dimensions of these two elements low, theinteraction between the prestress FV, contact face 22 and angle ofinclination α is selected such that the longitudinal bearing disk 8would not slip on the shaft 6 in the tangential direction even withoutthese two elements. Said elements therefore serve mainly to aid mountingand to ensure absorption of tangential forces in undesirable orunforeseen states.

1-14. (canceled)
 15. A rotor for a turbomachine, comprising: a shaft,and a longitudinal bearing disk arranged on said shaft as an element foran axial bearing for axially bearing the shaft, the longitudinal bearingdisk comprising: a first, cylindrical contact face for radial mountingon the shaft, and a second, conical contact face for automatic centeringon the shaft.
 16. The rotor as claimed in claim 15, wherein the secondcontact face is conical in an offset manner relative to radialcompression of the longitudinal bearing disk.
 17. The rotor as claimedin claim 15, wherein the second bearing face has an angle of inclinationrelative to the radial direction of the shaft of between 5° and 30°. 18.The rotor as claimed in claim 15, wherein the longitudinal bearing diskis mounted such that an increasing bearing force acts on the secondcontact face as the rotation speed increases.
 19. The rotor as claimedin claim 15, wherein the longitudinal bearing disk is mounted on theshaft without stress by way of the first contact face.
 20. The rotor asclaimed in claim 15, wherein the second contact face rests on a conicalmating face which is formed in the shaft.
 21. The rotor as claimed inclaim 15, wherein the second contact face is an end face of thelongitudinal bearing disk.
 22. The rotor as claimed in claim 15, whereinthe second contact face is provided for transferring at least the majorportion of the tangential forces from the shaft to the longitudinalbearing disk.
 23. The rotor as claimed in claim 15, further comprising arotation-prevention device for holding the longitudinal bearing disk ina desired tangential position by a positive-locking connection.
 24. Therotor as claimed in claim 23, wherein a positive-locking element of therotation-prevention device engages in an end face of the longitudinalbearing disk.
 25. The rotor as claimed in claim 24, wherein the end faceis arranged opposite the second contact face.
 26. The rotor as claimedin claim 23, wherein the rotation-prevention device has arotation-prevention ring which at least indirectly forms apositive-locking connection with the longitudinal bearing disk along adirection, and forms at least an indirect positive-locking connectionwith the shaft in the same direction.
 27. The rotor as claimed in claim15, further comprising a spring element for absorbing bearing forces onthe second contact face.
 28. The rotor as claimed in claim 27, whereinthe spring element obtains its spring action by a recess which iscompressed in the event of a springing operation.